JP2009516911A - Electrically pumped ND3 + doped solid state laser - Google Patents

Abstract

  It relates to the field of solid state lasers, and more particularly to laser cavities doped with rare earth ions, and also to the use of laser amplification structures, lasers, associated production methods and laser amplification structures. The amplification structure can be electrically excited and includes an active medium and at least two electrodes disposed on both sides of the active medium. The active medium comprising the first layer of silicon oxide is co-doped with silicon nanoparticles and rare earth ions.

Description

  The present invention relates to the field of solid state lasers, and more particularly to laser cavities doped with rare earth ions.

  The market for lasers is dominated by lasers based primarily on laser diodes and insulating materials (glass and quartz) doped with rare earths or transition metals.

  The laser diode is mainly composed of a diode using a semiconductor for the purpose of generating a light beam. Pumping is performed with the help of a current that enriches the holes of the generating medium on one side and the electrons on the other side. Light is generated at the junction by recombining holes and electrons. This type of laser does not have any cavity mirrors. Within a laser diode, the inversion distribution required to obtain the laser effect is possible using electrical excitation, improving the compactness of such a system. However, these systems differ from solid state lasers in terms of operation or structure, and the resulting physical problems.

A solid-state laser uses a solid medium such as quartz or glass as a photon generating medium. Quartz or glass is only a gain medium and is doped with at least one ion which is a laser medium (active medium, ie a medium in which the laser effect takes place, ie a phenomenon in which the doping element for light emission is excited and deexcited) Is done. The best known and most common of solid state lasers is YAG: Nd ³⁺ . Insulating materials doped with active ions (quartz and glass) require optical pumping with lamps or laser diodes, thus limiting their integration. On the other hand, their characteristics are different from and complementary to laser diodes (succinct, high energy pulses, strong brightness, spectral tunability, strong luminous power, etc.).

  Active media are also used in similar fields such as doped fibers, waveguide amplifiers and the like.

  The field of rare earth doped fibers has developed significantly with the creation of ultra high power lasers. Although the fibers provide great flexibility in use, they do not allow laser integration.

For integrated systems in the form of thin waveguide layers doped with active ions, research efforts are mainly focused on telecommunications amplifiers doped with Er ³⁺ and Tm ³⁺ around 1.5 μm. Similarly, extensive research work has been done on the production of thin waveguide lasers that can achieve high power levels. Such systems are described in patent applications such as, for example, International Application No. 065093 (WO-065093) and US Patent Application No. 2005/0195472. In this first application, a silicon oxide waveguide co-doped with silicon Si and rare earth atom nanoclusters (nanoparticles) absorbs visible light but not infrared radiation. Based on this principle, an optical pumping source is installed on the waveguide. The pumping light injected into the conducting tube excites the silicon nanoparticles (by electron-hole bonding), which in turn excites the rare earth elements. Such energy transfer between silicon nanoparticles and rare earth elements is referred to as “Nd nanocluster coupling strength and its effect on excitation / deexcitation of Nd ³⁺ luminescence in Nd-doped silicon-rich silicon oxide”. The title publication (Seo et at. Applied Physics Lelters, Vol. 83, No. 14, October 6, 2003) suggests an increase in effectiveness (several tens or even a hundredfold). It has been. At this time, the optical input signal is amplified in the conducting tube using the energy generated by the rare earth element, and comes out in the form of an amplified optical output signal.

  This system, like all systems containing silicon nanoparticles, requires the combination of a laser diode for optical pumping and a doped active medium that limits integration.

  The primary object of the present invention is to facilitate the integration of solid state lasers into more complex systems.

  Another object of the present invention is to provide a solid state laser as compact as possible.

  The presence of a laser diode for optical pumping also means energy waste due to its efficiency.

  Another object of the present invention is to reduce the power consumption of solid state lasers and thus increase the efficiency of these systems.

  Although laser diodes are inexpensive, the production of solid state laser systems still requires economic expenditure.

  Another object of the present invention is to reduce the manufacturing cost of the solid state laser without making it more complicated.

  In the second application mentioned above, the optical amplifier consists of a waveguide made of silicon doped with erbium ions, said waveguide being arranged on the opposite wall of the conduit. Powered by pumping energy, which can be either optical or electrical, using two electrodes, or by Raman scattering. In embodiments involving electrical pumping, erbium ions are excited by an electric field applied between the two electrodes. However, erbium ions are less sensitive to electric fields and the only possibility for direct excitation of active erbium ions is that photon absorption by this ion (as opposed to electrical excitation). Excitation does not actually work, so the system consumes a lot of energy to get a sufficient number of excited ions.

  Accordingly, another object of the present invention is to provide an electrically pumped laser solution that allows easier excitation of doping ions, particularly a solution with low energy consumption while improving efficiency.

  It is also pointed out that the operation of these similar systems (conducting amplifiers, laser fibers, etc.) is highly dependent on the input optical signal being amplified. In contrast, solid state lasers with which the present invention is concerned do not require the use of an input optical signal to emit an output signal.

  One of the above-mentioned objects is achieved by using silicon nanoparticles in the active medium, which are nanoparticles sensitive to an electric field passing through the active medium. Thus, the present invention relies on the electrical excitation of active ions using semiconductors, unlike the known prior art.

  For this purpose, the present invention inter alia, in a laser amplification structure comprising an active medium and at least two electrodes arranged on both sides of the active medium, said active medium being co-doped with silicon nanoparticles and rare earth ions. And a laser amplification structure comprising a first layer of silicon oxide (hereinafter referred to as a co-doped layer). In practice, the aforementioned electrodes are connected to a power source, and thus in use, a current flows through the aforementioned first layer to excite the aforementioned silicon nanoparticles. This laser amplification structure can be electrically excited.

  Silicon nanoparticles have been found to be sensitive to currents that run through the active medium. Thus, the silicon nanoparticles are excited by an electric current and then transfer their excitation energy to the rare earth ions as described in the Seo et al. Publication mentioned above. At this time, conventional mechanisms for stimulated laser emission are applied to emit electromagnetic radiation by deexcitation of rare earth ions. In this respect, it can be seen that the silicon nanoparticles act as electrical dopants with the ability to transfer their energy to other dopants.

  Such a structure thus makes it possible to do without a secondary light source (pumping laser diode).

  One field of use of these structures is photonics, where they are generally integrated into semiconductor circuits.

  For this purpose, the aforementioned first layer is thin in the semiconductor sense, that is, generally deposited on a much thicker substrate to benefit from the mechanical properties of this substrate. It is envisioned to be a layer having a thickness of less than or substantially equal to 1 micrometer (1 μm). In this manner, the resulting structure provides a great deal of compactness, so that it can be easily integrated into a device or integrated circuit. In one embodiment, the active medium is composed solely of this co-doped thin layer and thus has a thickness of substantially 1 micrometer.

  Due to the size of the nanoparticles compared to the thickness of the silicon oxide layer, it is difficult to create a homogeneous co-doped layer.

  To solve this problem, it is possible to use a multilayer structure that alternates between undoped and co-doped thin layers using rare earth ions (and possibly nanoparticles).

  For this purpose, it is envisaged that the active medium further comprises a thin layer of silicon oxide not doped with rare earth ions on which the first layer is deposited. Similarly, it is envisaged that the active medium includes a second layer of silicon oxide doped with rare earth ions and silicon nanoparticles on which the undoped layer is deposited. In this configuration, the undoped layer must be thin because it constitutes an insulating layer and must ensure the tunneling effect necessary for current circulation between the two co-doped layers. As an example, a thickness of 5 nm or less is recommended for the undoped layer.

  The present invention is not limited to an active medium consisting of two co-doped layers and one undoped layer, but also provides an active medium having a number of co-doped layers separated by two by the undoped layer. Multi-layer structures are provided, including dozens or even hundreds, and in exceptional cases thousands. A multilayer active medium is preferably chosen in which the two outer layers (top layer and bottom layer) are co-doped with Si nanoparticles and rare earth ions. The active medium thus formed contains all the co-doped layers (and thus has the ability to generate light waves).

  In the multi-layer embodiment, the electrodes are positioned parallel to the layers, each electrode covering all or part of the surface of the upper and lower layers (outer layers) of the active medium. The bottom electrode can either be in direct contact with the active medium, i.e. between the active medium and the growth substrate, or it can be positioned on the underside of the substrate and this substrate allows electrical conduction.

Commonly used active media have a thickness of a few millimeters. The size of the sample can be changed to a few hundred micrometers for the purpose of either improving dissipation (thin discs) or increasing compactness (microchips). Nd ³⁺ ions are well suited for microchip devices because of their larger effective absorption and emission cross sections.

  Similarly, in a design that facilitates integration of the structure, the active layer of the structure has a thickness of approximately a few μm, preferably around 1 micrometer, according to the refractive index and current injection characteristics for guiding the light in the layer. . In particular, when a single co-doped thin layer is used in the active medium, the thickness is selected to be approximately 1 μm or less. It should be borne in mind that the active layer in this case is an active medium composed of a multilayer assembly (co-doped layer, undoped layer).

  For the purpose of optimizing energy transfer between silicon nanoparticles and rare earth ions, the present invention provides a co-doped layer having a nanocrystalline or amorphous structure, and the rare earth ions and Si nanoparticles in the active medium described above. It is assumed that the average separation distance is 0.4 nm or less.

  The amplification structure is implemented in the laser as one element of a resonant optical cavity. For this purpose, it is provided with a reflective surface such as a mirror. Said active medium preferably comprises a Bragg grating arranged substantially perpendicular to said electrode, said grating being germanium Ge ions photoinscribed into said co-doped layer (s). It is made with. In order to increase the effectiveness of the system, all co-doped layers of the active medium preferably include Bragg gratings aligned with each other. These gratings optionally close an optical cavity that acts as a mirror for electromagnetic emission of excited rare earth dopant ions. Preferably, these are substantially directly below the edge of the electrode, and in some cases if the electrode covers only part of the surface of the active medium (at the edge of the co-doped layer, the edge It is recommended to install beyond this. In practice, two parallel Bragg gratings are on both sides of the electrode and face each other to define a laser light cavity.

  Preferably one of the gratings is semi-reflective. In an embodiment that includes only one co-doped layer, two gratings are placed within this same layer, perpendicular to the top and bottom surfaces (within thickness) of said layer.

  In addition, one of the aforementioned electrodes is made from gold (Au) that provides significant electrical conductivity while minimizing energy loss. The other electrode can be made of a Ni-Cr alloy.

  In one embodiment, the electrodes each include a conductive layer, for example made from ITO (Indium Tin Oxide), each adjacent one of the opposing faces of the active medium.

According to a different embodiment, the rare earth ions are selected from Nd ³⁺ , Yb ³⁺ , Er ³⁺ , Tm ³⁺ and Ho ³⁺ .

In particular, Nd ³⁺ is rapidly gaining value as a major active ion for laser equipment. With the success of YAG: Nd ³⁺ , the transition to 1.064 μm has become one standard for laser emission for applications where wavelength is not a selection criterion. Among other rare earth ions, Yb ³⁺ having emission in the same wavelength range should be mentioned. For a long time, optical pumping of Nd ³⁺ ions has a large pumping efficiency because the ions have numerous energy levels that exceed the emission laser level, and these levels absorb most of the light emitted by the lamp. It was carried out by a lamp with The development of AlGaAs diodes that emit light at around 800 nm in the 1980s requires that lasers using laser diode pumping be gradually replaced by Nd ³⁺ lasers using lamp pumping. Nd ³⁺ ions used primarily for their emission around 1.06 μm are systems where most of the other ions (Yb ³⁺ , Er ^3+, etc.) are almost accompanied by three levels. Since the terminal level ( ⁴ I _11/2 ) has a life several orders of magnitude shorter than the laser emitter level ( ⁴ F _3/2 ), a laser system with four levels that can obtain the inversion distribution very easily is obtained. It is a type of including. Accordingly, a preferred embodiment of the present invention is provided using Nd ³ ions. For these “other” ions, the laser terminal level is close to the fundamental level of ions that require more pumping to implement the population inversion required to reach the laser threshold. Receiving heat distribution. Thus, the advantage provided by using Nd ³⁺ dopant ions is that it reduces the power consumption to achieve the desired pumping. Furthermore, it is necessary to optimize the length of the active medium in order to prevent reabsorption of the laser emission. Effective absorption and stimulated emission cross section play a very important role. For Nd ³⁺ ions, these effective absorption and emission cross sections are much larger than other ions, especially Yb ³⁺ , for a given gain medium.

  The invention also relates to an optical laser comprising a constant current source connected to the aforementioned electrode and an optical laser cavity with an amplification structure. Strictly speaking, the constant current source is arranged to pass a current through the active medium for the purpose of exciting the silicon nanoparticles during use, particularly in the first layer. According to the mechanism described above, the rare earth ions are themselves excited by energy transfer from the Si nanoparticles to the rare earth ions.

  The laser thus produced is as compact as a laser diode, while providing additional features such as very high energy pulses, spectral purity and stability, regardless of temperature or manufacturing conditions.

The invention also relates to a method of manufacturing a laser amplification structure,
A first step of depositing a layer of silicon oxide co-doped with silicon nanoparticles and rare earth ions on a substrate; and on both sides of the active medium, optionally on at least a portion of said co-doped layer It also relates to a method comprising the step of depositing electrodes.

  Several alternatives are conceivable for depositing the electrodes. In the first alternative, the side of the active layer opposite to the substrate and the other metal electrode behind it (if this is not an insulating obstacle that prevents electrical conduction in the active medium) In some cases, it is envisaged to deposit a metal electrode on a co-doped layer, but in some cases on a multi-layer assembly mentioned elsewhere in this specification.

  The second alternative envisages depositing a transparent conductor layer on two opposing surfaces of an ITO (indium tin oxide) active layer. In particular, it is possible to deposit an ITO layer on the substrate before depositing the active layer. At this time, metal contacts can be deposited on these transparent conductive layers to allow connection to a constant current source. The assembly composed of a transparent conductive layer and contact terminals forms an electrode that is used for electrical excitation of the co-doped active medium.

  Similarly, by depositing a conductive layer on the aforementioned substrate and by the fact that the second electrode is deposited after the active medium deposition step on the opposite surface of the active medium, one It is also envisaged that the electrode is applied prior to the application stage of the active medium.

  In one embodiment, the deposition step is performed by reactive magnetron co-sputtering of at least one target comprising a first silicon oxide material and a second rare earth material. The second material can be placed on a portion of the target. In other words, it is envisaged to use multiple targets, each with a single type of material, in a confocal co-sputtering process.

  During this deposition phase, the substrate acts as an anode and the target acts as a cathode. By this mechanism, a plasma is created between the anode and the cathode, allowing for the separation of silicon elements, oxides and rare earth elements that condense on the substrate.

  The reactive magnetron co-sputtering process is very suitable for forming thin layers. These processes thus enable the production of substantially planar structures suitable for semiconductors and for the production of electrically excited planar lasers.

According to two variants, said at least one target is a single silicon oxide target carrying a plurality of rare earth oxide wafers (variant 1), said at least one target being a silicon Si target, Including the aforementioned target of the first silicon oxide SiO ₂ material and the aforementioned target of the second rare earth material (variation 2).

  The second variant has the advantage of performing normal co-sputtering of three parallel cathodes and limiting the interaction between the various elements of the target in a global sense (more difficult to control) Have

The nature of the plasma used during the co-sputtering step is highly dependent on the composition of the co-doped layer that is formed. Thus, it is envisioned that this co-sputtering step is performed in a vacuum enclosure containing argon and / or hydrogen and / or nitrogen plasma. In the case of reactive sputtering, the presence of hydrogen makes it possible to reduce silicon oxide so as to include silicon surplus (silicon nanoparticles) in the same deposited SiO ₂ gain medium. Rare earth ions are introduced into the Si—SiO ₂ composite using plasma. For this purpose, it is assumed that the hydrogen ratio in the plasma is comprised between 10% and 90%. This ratio facilitates the formation of larger or smaller amounts of Si crystal nuclei and thus the density of nanoclusters within the deposited layer, depending on the deposition conditions (plasma pressure, substrate temperature, interelectrode distance, etc.).

In general, plasma-containing hydrogen is used in the absence of a pure silicon target. This is true either in the hypothesis that the rare earth oxide is on a SiO ₂ target or in the hypothesis of two SiO ₂ and Nd ₂ O ₃ targets. In the latter hypothesis, a mixture of Ar + H ₂ is used to add silicon Si to the growing co-doped layer (for a single layer), otherwise silicon for the co-doped layer enriched with nanoclusters. A pure argon plasma is used for a growing silicon layer in which the Ar + H ₂ mixture is not doped with rare earth ions to add Si.

On the other hand, when three targets -Si, SiO ₂ and Nd ₂ O _3- are deposited, the target Si supplies nanoclusters with Si without the need to reduce SiO ₂ silicon, so the presence of hydrogen Is not required at all.

Another parameter to be taken into account is the target surface area occupied by the aforementioned rare earth material, preferably comprised between 3 and 30% of the total surface area of the target, depending on the rare earth ions in question. This parameter makes it possible to change the ratio of rare earth ions in the final deposit in relation to silicon surplus (nanoparticles). For example, for erbium ions, the optimum surface area is comprised between 23% and 26%, but for Nd ³⁺ ions it should not exceed 12%.

  In order to obtain a Bragg grating as described above, it is also envisaged that at least one wafer-containing germanium (Ge) is placed on the target during the co-sputtering step. Similarly, by reactive magnetron co-sputtering, germanium ions are extracted from the wafer and deposited in the layer being deposited. The germanium ions thus deposited are inscribed to form the aforementioned lattice. Photoinscription is performed using a UV laser. An interference pattern is projected onto a portion of the waveguide containing Ge, inducing irradiated and non-irradiated zones, thus forming a grating. Irradiation induces the formation of a color center that modifies the refractive index of the medium. In this way, a change of zones with different refractive indices is obtained, which acts as a mirror.

  For this purpose, do not place the germanium wafer until the correct moment to form the Bragg grating, that is, when the co-doped layer is deposited (because there is no light emission in the undoped layer where no rare earth ions are provided) May be assumed.

According to one variant, it is envisaged to deposit Ge throughout the growing co-doped layer. Ge ions are inactive from the viewpoint of rare earth ions (eg Nd ³⁺ ). At this time, the grating is inscribed only in the desired zone (layer edge).

  Moreover, molecular defects that may be created when depositing the layer must be repaired or reduced. To this end, the method also includes the step of annealing the layer thus formed at a temperature comprised between 800 ° C. and 1100 ° C. for at least 10 minutes.

  According to one embodiment, the method comprises the step of depositing a doped polycrystalline silicon layer N on said doped layer before depositing said electrode.

In order to produce the multilayer active medium described above, the method comprises:
A step of depositing a co-doped layer and a subsequent deposition step to form a layer of undoped silicon oxide on the co-doped layer can be included in succession.

  The deposition of the co-doped layer is a reactive magnetron co-sputtering stage of at least one target comprising a first silicon oxide material and a second rare earth material, wherein the second material is a portion of the target. And the subsequent deposition step described above is for the silicon oxide target in a vacuum enclosure containing an argon plasma to form an undoped silicon oxide layer over the co-doped layer. It is assumed that it is a reactive magnetron sputtering stage.

  Because the reaction parameters are different, different cathodes are selected for each of the co-sputtering and sputtering stages.

  More precisely, the method includes multiple alternations of co-sputtering steps and sputtering steps to form a multilayer structure, the first and last steps performed preferably apply a co-doped layer. The electrode is deposited on the top surface of the layer opposite the substrate in the structure (the other is on the back of the substrate).

According to two variants, during the aforementioned sputtering stage,
Argon plasma is pure argon plasma, thus making it possible to obtain an undoped layer without any Si nanoparticles;
The plasma described above is enriched with hydrogen to include excess Si in the undoped insulating layer. Thus, electrical conduction in the thin insulating layer is facilitated, and a tunnel effect is possible.

Furthermore, the rare earth ions are of at least one type selected from the ions of Nd ³⁺ , Yb ³⁺ , Er ³⁺ , Tm ³⁺ and Ho ³⁺ .

  It is further envisaged to produce a silver waveguide to allow lateral guidance of light. These silver waveguides can be manufactured by etching once the layer has been deposited. Starting from a multilayer device, silver waveguides from several nm to several tens of nm are etched using a mask. A suitable technique for this is reactive ion etching (RTE).

  The invention also relates to a method of operating a laser comprising an optical cavity with a laser amplification structure and a constant current source, wherein at least two of said laser amplification structures are arranged on both sides of the active medium and said active medium. The active medium includes a first layer of silicon oxide co-doped with silicon nanoparticles and rare earth ions; the constant current source is connected to the electrode, and the electrode And a method of passing a current through the active medium by applying a power supply to the terminal.

  The invention also relates to the use of a laser amplification structure comprising a layer of silicon oxide electropumped and codoped with silicon nanoparticles and rare earth ions as a laser amplifier. This use is equally applicable to lasers or laser fibers.

  The invention will be better understood from the following detailed description and the accompanying drawings.

The following example shows the mechanism of effective energy transfer between Si nanoparticles and Nd ³⁺ ions for thin layers produced by reactive magnetron sputtering and thus allowing the production of electrically excited planar lasers And show optimization.

The confinement of carriers (excitons) inside the silicon nanoparticles inserted in the silica gain medium makes it possible to obtain visible luminescence by electrical or optical excitation of such composite systems. Extensive work has been done on the study of silicon nanoparticles associated with Er ³⁺ ions to produce amplifiers in the field of wavelengths suitable for telecommunications (1.54 μm). There is effective energy transfer between the nanoparticle and the rare earth, and thus it is possible to emit at an intensity 100 times that which is typical in the absence of nanoparticles.

A silica gain medium containing silicon nanoparticles associated with Nd ³⁺ ions is used for the fabrication of integrated lasers. In fact, it has recently been demonstrated that there is a transfer between Si nanoparticles and Nd ³⁺ ions in a layer produced by PECVD (plasma chemical vapor deposition) assisted by ECR (electron cyclotron resonance) [ Seo et al. Appl. Phys. Lett., 83, 2778 (2003); "Nd-nanocluster coupling strength and its effect on excitation / de-excitation of Nd3 ⁺ luminescence in Nd-doped silicon-rich silicon oxide" ]. The present invention allows the electrical excitation of silicon nanoparticles that transfer their energy to the Nd ³⁺ ion, thus creating an inversion distribution between the two laser levels of this ion. Therefore, depending on the properties of the gain medium (material and dopant), laser emission at around 1.1 μm can be obtained.

  That is the case when a thin layer of silica glass co-doped with neodymium and Si nanoparticles is produced by reactive magnetron co-sputtering. These waveguiding layers create an electrically pumped laser system after electrode etching and deposition, which can emit light around 1.1 μm. This approach is compatible with silicon technology and is completely consistent with the current trend of producing compact systems that are easily integrated.

  A reactive co-sputtering technique used to deposit thin layers among others is schematically represented in FIG.

Pure silica target 10 includes a variable number of Nd ₂ O ₃ (rare earth oxide) wafers 11 for adjusting the concentration of Nd ³⁺ ions contained in the deposited layer, as well as their gaps. Ge or GeO ₂ component 12 is included to allow the silicon sensitivity to be increased by reducing [Nishi et al., Optics Lett., 20, 10, 1184 (1995) ); see "UV induced chemical reactions through the 1 and 2-photon absorption process GeO ₂ -SiO ₂ glass"]. In this way, the Bragg grating acts as a future mirror for the optical cavity and is photoinscribed at both ends of a silicon waveguide doped with Nd ³⁺ ions and contains Si nanoparticles. The excess silicon contained in the layer is obtained through the reactivity of the plasma consisting of a mixture of ionized argon and hydrogen that sputters and interacts with the SiO ₂ —Nd ₂ O ₃ —Ge compound. With the reduction of hydrogen with respect to oxygen in mind, such a method results in a lack of oxygen in the layer, thus allowing the amount of excess silicon to be controlled by modifying the hydrogen partial pressure. To do. In addition to this parameter, the use of reactive gases such as hydrogen leads to the phenomenon of selective etching of the growing layer, thus encouraging multiple nucleation sites for Si nanoparticles. The resulting higher density of nanoparticles ensures a higher coupling strength with Nd ³⁺ ions and thus a higher proportion of optically active ions. The deposition is performed at room temperature with a total pressure of gas not exceeding 6 × 10 ⁻² Torr, with power varying between 50 w and 120 w. With this configuration, gas ionization allows elements to be detached from the target and deposited on the substrate (anode) 13.

The post-deposition heat treatment is carried out between 800 ° C. and 1100 ° C. and depending on the time under pure Ar or N ₂ flow.

The absorption spectrum of Nd ³⁺ ions derived from a SiO ₂ —Nd film produced by magnetron sputtering (no excess silicon present) is presented in FIG. This spectrum reveals the presence of strong absorption (20) of Nd ³⁺ ions at 800 nm, which makes it possible to predict energy transfer between excited Si nanoparticles and Nd ³⁺ ions. It has become. Furthermore, the 488 nm line supplied by the argon laser is a line with very low resonance for Nd ³⁺ ions, so that this excitation wavelength can be used to account for this energy transfer with this rare earth ion. You can also see that

FIG. 3 shows the change in the photoluminescence intensity of Nd ³⁺ ions according to the hydrogen ratio in the plasma (r _H = R _H2 / P _H2 + P _Ar ) for thin films produced with an RF power of 60 w. It can be seen that the film _deposited with the highest hydrogen ratio r _H = R _H2 / P _H2 + P _Ar has the highest intensity (30) at the splitting emission peak. As already mentioned, this is due to the maximum density of Si nanoparticles acting as a relay for exciting Nd ³⁺ ions. The role of the sensitizers played by the Si nanoparticles is due to the significant increase in the strength of the silicon-containing film compared to those produced in pure (or nearly pure) argon plasma (31) and thus containing little excess Si. Clearly shown.

The effect of the heat treatment applied on the release of Nd ³⁺ ions is presented in FIG. The increase in temperature has a significant advantage on one emission peak at the expense of one emission peak while increasing its intensity by approximately one digit.

A simple linear waveguide with or without cladding is obtained after etching and depositing the electrodes to allow current injection. These electrodes (Al, Au, Al—Si alloy, etc.) are all deposited along the waveguide and on the back side of the substrate. Electrical excitation leads to the formation of excitons inside the Si nanoparticles, which either emit light at 800 nm by recombination or transfer its energy to nearby Nd ³⁺ ions, and thus the desired properties of this rare earth element. It is possible to emit light at a wavelength of.

Electrical excitation within such systems can be facilitated using multilayer structures. In fact, in order to allow optimal electrical excitation of Si nanoparticles embedded in an insulating gain medium (SiO ₂ ), Si nanoparticles have a “tunnel distance” (2- It must have a density sufficient to be separated from each other by a distance smaller than (around 4 nm). In addition, these nanoparticles are then 5-6 nm so as to preserve this quantum confinement property of the carriers that allow them to act as their effective sensitizer towards the immediate rare earth ions. It must have a size less than front and back and be surrounded by oxide.

  The reactive magnetron sputtering technique used to deposit these multilayers is shown in schematic form in FIG. This makes it possible to control the thickness of the different types of deposited layers as well as the location of the rare earth ions so as to optimize their emission. This is in two aspects: technical aspects related to the use of two cathodes (50a and 50b) and alternating deposition by sequential rotation of the substrate-holder (anode 51), and in the plasma, and thus silica. Characterized by the reactive aspect associated with the presence of hydrogen interacting with the target. The two targets are made of silica, and one has a variable number of rare earth oxide wafers (52) to adjust the concentration of the rare earth it contains.

The deposition sequence is as follows:
If the substrate (or anode) is facing the target on which the rare earth oxide component is placed (position B), the deposition is performed under a hydrogen-mixed argon plasma (˜1: 1) (53). ). With the hydrogen reducing power with respect to oxygen from the silica target in mind, the deposited layer now contains excess silicon next to the rare earth ions incorporated by co-sputtering of the oxide wafer.

The deposition of the SiO ₂ layer is performed by placing the substrate on the opposite side of the pure silica target under pure argon plasma (position A) (54).

  These sequences are repeated as many times as necessary to obtain the predetermined structural features and optical properties for the produced film.

  FIG. 6 shows a multilayer structure in which three layers 60 co-doped with Si nanoparticles and rare earth ions are separated by two insulating silicon oxide layers 61. A Bragg grating 62 is inscribed in each of the two outer layers to form an optical cavity of the laser. The electrodes 63 are installed on both sides of the multilayer active medium and are supplied with power by a constant current source G that allows current to flow through the layer overlap. The grating 62a (left side of the figure) on one side of the structure is semi-reflective and the grating 62b on the opposite side of the structure is a nearly perfect mirror. In this way, light emission 64 from the laser structure excited by the circulating current is carried out on the same side (left side in the figure).

  FIG. 7 shows another structure according to the present invention in which certain features associated with the electrodes can be combined in whole or in part with the structure of FIG.

  The deposition of the various layers of this structure is performed by a reactive magnetron sputtering method as described above.

The structure is deposited in layers on a silicon substrate (70). This includes the following in the following order:
A first intermediate layer (buffer) 71 made of silica SiO ₂ having a thickness of around 5 μm and a medium refractive index substantially equal to 1.45;
A transparent conductive layer 72 of ITO (Indium Tin Oxide) having a thickness of less than 100 nm and a refractive index approximately equal to 1.9;
Active medium comprising a layer co-doped with silicon nanoparticles and rare earth ions having a thickness comprised between 500 nm and 1 μm and a refractive index comprised between 1.5 and 2 73. A multilayer structure as described with reference to FIG. 6 can also be provided;
Preferably, on the side of the active medium other than the side that acts as the laser entrance (typically the side with a partially reflecting Bragg mirror), on a part of the layer 72 not covered by the active medium 73 One or more metal terminals 74. This terminal 74 can be made of metal by removing a portion of the active medium 73 from the ITO layer, or if deposition of the active medium 73 is initially planned for only a single portion of the ITO layer 72. Can be deposited by localized deposition;
A second transparent ITO conductive layer 75 on the active medium having features similar to the first ITO layer 72;
A second intermediate layer 76 of silica SiO ₂ having an approximate thickness of 200 nm and a medium refractive index of around 1.45. This layer is deposited only on a portion of the ITO layer 75;
One or more metal terminals 76 in direct contact with the second ITO layer 75.

  The metal terminal (s) 74 in contact with the first ITO layer 72 is connected to the terminal of the constant current source 78, and the metal terminal 77 in contact with the second ITO layer 75 is connected to the constant current source. Connected to the other terminal of 78, current flows through the active medium 73 as a result of the conductivity of the ITO layers 72 and 78. In this embodiment, each ITO layer and metal terminal assembly is considered to be an electrically excitable laser electrode.

  This causes a photon distribution (obtained as a result of deexcitation of the rare earth ions causing the laser phenomenon) inside the waveguide formed by the active medium.

  This structure has the advantage of overcoming the potential barrier induced by the presence of an intermediate silica layer between the substrate and the active layer.

  A lower index of refraction is used on both sides of the waveguide to ensure the guidance of light in the active medium (amplification medium) (layers as low as 1.5 in the active layer 73). 71 and 76 have a refractive index of 1.45). In order to reduce the influence of the transparent conductive layers 72 and 75 on the induction and amplification of the optical signal, and in particular to avoid losses due to evanescent waves, the transparent layer is selected to be as thin as about tens of nanometers. The Moreover, these layers potentially represent potential barriers to overcome for charge carriers. Thus, the layer is very thin, sometimes in the order of a few nm to 10 nm.

The following rare earths can benefit from the role of effective sensitizers performed by Si nanoparticles:
Yb ³⁺ ions for light emission around 1 μm.
Er ³⁺ ions for light emission at 1.54 μm, which will allow light transport and optical transmission of information, especially in computers.
Tm ³⁺ ions for luminescence close to 2 μm for applications including distance measurement in the medical field, eye protection.
Also 2μm for light emission before and after, Ho ³⁺ ions for the same FIELD and therefore Tm ³⁺ ions.

In addition, different types of gain media can be used:
Silicon dioxide SiO ₂ ;
Silicon oxide SiOx;
Silicon oxynitride SiOxNy.

  For silicon oxynitride gain media, it is possible to allow the aforementioned plasma to be enriched with nitrogen, thus forming an oxynitride gain medium that facilitates electrical conduction therein in the presence of Si nanoparticles. is there. The presence of nitrogen can complement the presence of hydrogen.

FIG. 2 is a schematic representation of a substrate-anode and target-cathode inside a deposition frame in a co-doped thin layer deposit configuration. The magnetron sputtering is a graph showing the absorption spectrum of Nd ³⁺ ions of SiO ₂ -Nd the films deposited. It is a graph which shows the influence of the hydrogen ratio in a plasma with respect to the luminescence intensity of Nd3 ⁺ ion in the film annealed at 900 ^degreeC . FIG. 6 is a graph showing the PL intensity of a film produced with 80% H ₂ in plasma and annealed under various conditions. Figure 2 is a schematic representation of a substrate-anode and two target-cathodes within a deposition frame for multi-layer deposition according to the present invention. FIG. 4 shows a multilayer embodiment implemented according to the present invention. FIG. 4 shows a multilayer embodiment implemented according to the present invention.

Claims (28)

  A laser amplification structure comprising an active medium and at least two electrodes disposed on opposite sides of the active medium, wherein the active medium comprises a first layer of silicon oxide doped with rare earth ions, the first silicon A laser amplification structure in which the layer is co-doped with silicon nanoparticles and rare earth ions.   The structure of claim 1, wherein the active medium further comprises a thin layer of silicon oxide that is not doped with rare earth ions, on which the first layer is deposited.   The active medium comprises a plurality of layers of silicon oxide co-doped with silicon nanoparticles and rare earth ions, wherein the co-doped layer is separated by an undoped silicon oxide layer, The structure according to claim 1 or 2, wherein the bottom layer is a co-doped layer.   The structure according to any one of claims 1 to 3, wherein the co-doped layer has a structure in which an average distance separating silicon nanoparticles and rare earth ions in the active medium is 0.4 nm or less. 2. The structure of claim 1 wherein the rare earth ion is of at least one type selected from the ions Nd3 ⁺ , Yb3 ⁺ , Er3 ⁺ , Tm3 ^+, and Ho3 ⁺ .   The active medium includes a Bragg grating disposed substantially perpendicular to the electrode, the grating being made of germanium Ge ions photoinscribed into the co-doped layer (s). The structure of claim 1.   The structure of claim 1 wherein each of said electrodes comprises a conductive layer adjacent to one of the opposing faces of the active medium.   The structure of claim 1 wherein the co-doped layer (s) is a thin layer.   An optical laser comprising an optical cavity comprising the amplification structure according to claim 1 and a constant current source connected to the electrode.   The laser according to claim 9, wherein the constant current source is arranged to pass a current through the active medium for the purpose of exciting the silicon nanoparticles during use. A method of manufacturing a laser amplification structure, comprising:
A first step of depositing a layer of silicon oxide co-doped with silicon nanoparticles and rare earth ions on a substrate; and depositing electrodes on both sides of the active medium.   By depositing a conductive layer on the substrate, an electrode is deposited before the step of depositing the active medium, and a second after the step of depositing the active medium on the surface opposite the active medium. The method of claim 11 wherein a plurality of electrodes are deposited.   The first step is performed by reactive magnetron co-sputtering of at least one target comprising a first silicon oxide material and a second rare earth material, and the second material is disposed on a portion of the target. The method according to claim 11.   The method of claim 13, wherein the at least one target is a single silicon oxide target having a plurality of rare earth oxide wafers thereon.   14. The method of claim 13, wherein the surface area of the target occupied by the rare earth material is comprised between 3% and 30% of the total surface area of the single target. The method of claim 13, wherein the at least one target comprises a silicon Si target, a target of the first silicon oxide SiO ₂ material, and a target of the second rare earth material.   The method of claim 13, wherein the co-sputtering step is performed in a vacuum enclosure comprising ionized argon and hydrogen plasma.   The method according to claim 17, wherein the hydrogen ratio in the plasma is comprised between 40% and 90%.   14. The method of claim 13, wherein at least one wafer comprising germanium (Ge) is also placed on the target during the co-sputtering step.   The method according to any one of claims 11 to 19, further comprising annealing the layer thus formed at a temperature comprised between 800-1100C for at least 10 minutes. The step of depositing the active medium is
Depositing a co-doped layer; and a subsequent deposition step to form a layer of undoped silicon oxide on the co-doped layer;
The method according to claim 11, comprising:   The deposition of the co-doped layer is a reactive magnetron co-sputtering stage of at least one target comprising a first silicon oxide material and a second rare earth material, the second material being on a portion of the target. The method of claim 21, wherein the subsequent deposition step is a reactive magnetron sputtering step of a silicon oxide target to form an undoped silicon oxide layer over the co-doped layer. .   In order to form a multi-layer structure, it includes a plurality of alternations of co-doped layers and subsequent deposition steps, wherein the first and last steps of the plurality of alternations are simultaneous for depositing a co-doped layer The method of claim 22, wherein the method is a sputtering step.   23. The method of claim 22, wherein the argon plasma is a pure argon plasma during the sputtering step.   24. The method of claim 23, wherein the plasma is hydrogen enriched during the sputtering step. The method according to claim 11, wherein the rare earth ions are of at least one type selected from ions of Nd ³⁺ , Yb ³⁺ , Er ³⁺ , Tm ³⁺ and Ho ³⁺ . A method of operating a laser including an optical cavity with a laser amplification structure and a constant current source,
A first layer of silicon oxide wherein the laser amplification structure includes at least two electrodes disposed on both sides of the active medium and the active medium, the active medium being co-doped with silicon nanoparticles and rare earth ions Including
The constant current source is connected to the electrode;
Flowing a current through the active medium by applying a power supply to a terminal of the electrode.   Use as a laser amplifier of a laser amplification structure comprising a layer of silicon oxide electrically pumped and codoped with silicon nanoparticles and rare earth ions.

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